I took out my camera after quite a few months of not having used and noticed something wrong with the LCD screen. When I turn on the camera, the screen just shows vertical grey lines throughout the screen. The lines moves around as I move the camera around. I can still take photos but cannot view them, or anything else, on the screen for that matter (i.e. menus etc). Not even sure how it has happened as the camera has just been in its case the last few months.

Sounds like the super thin wire that connects the screen to the camera sensor or internals probably came loose or something is pressing against the connection between screen and internals.

The only other thing I can think of is the LCD itself has been physically damaged in some way, as in heat, a drop, moisture, cold or a number of possible culprits.

Since you havent mistreated your camera, I would suggest taking the camera to Nikon themselves or call them up and ask what the cause of your symptoms are and see if they can get it repaired under warranty. LCD panels now are relatively cheap and even outside of warranty, they wont set you back so much - but break the internals or the lens etc.... well, better off calling your insurance company